Amphoteric liposomes

ABSTRACT

A serum-stable mixture of lipids capable of encapsulating an active agent to form a liposome, said mixture comprising phosphatidylcholine and phosphatidylethanolamine in a ratio in the range of about 0.5 to about 8. The mixture may also include pH sensitive anionic and cationic amphiphiles, such that the mixture is amphoteric, being negatively charged or neutral at pH 7.4 and positively charged at pH 4. Amphoteric liposomes comprising such a mixture may be used for encapsulating nucleic acid therapeutics, such as oligonucleotides and DNA plasmids. The drug/lipid ratio may be adjusted to target the liposomes to particular organs or other sites in the body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 11/521,857, filed on Sep. 15, 2006, which claims priority from U.S. Provisional Application Ser. No. 60/717,199, filed on Sep. 15, 2005; U.S. Provisional Application Ser. No. 60/717,291, filed on Sep. 15, 2005; U.S. Provisional Application Ser. No. 60/717,293, filed Sep. 15, 2005; European Application No. 05020218.3, filed on Sep. 15, 2005; European Application No. 05020217.5, filed on Sep. 15, 2005; European Patent Application No. 050202167.7, filed on Sep. 15, 2005; PCT Application No. PCT/EP2005/011905, filed on Nov. 4, 2005; PCT Application No. PCT/EP2005/011908, filed on Nov. 4, 2005; U.S. application Ser. No. 11/266,999, filed on Nov. 4, 2005 (abandoned); U.S. application Ser. No. 11/267,423, filed on Nov. 4, 2005 (abandoned); European Application No. 06113784.0, filed on May 10, 2006; and European Application No. 05090322.8, filed on Nov. 21, 2005. The contents of each of these applications are incorporated herein by reference in their entireties.

Each of the applications and patents cited in this text, as well as each document or reference cited in each of the applications and patents (including during the prosecution of each issued patent; “application cited documents”), and each of the U.S. and foreign applications or patents corresponding to and/or claiming priority from any of these applications and patents, and each of the documents cited or referenced in each of the application cited documents, are hereby expressly incorporated herein by reference. More generally, documents or references are cited in this text, either in a Reference List before the claims, or in the text itself; and, each of these documents or references (“herein-cited references”), as well as each document or reference cited in each of the herein-cited references (including any manufacturer's specifications, instructions, etc.), is hereby expressly incorporated herein by reference. Documents incorporated by reference into this text may be employed in the practice of the invention.

FIELD OF THE INVENTION

The present invention relates to amphoteric liposomes and has particular reference to such liposomes having improved stability in human or animal serum. The present invention also comprehends mixtures of lipids capable of encapsulating active agents or ingredients such, for example, as drugs to form liposomes and pharmaceutical compositions comprising such liposomes.

BACKGROUND OF THE INVENTION

Oligonucleotides represent a novel class of drugs that can very specifically down-regulate or interfere with protein expression. Such oligonucleotides include antisense, locked nucleic acids (LNA), peptide nucleic acids (PNA), morpholino nucleic acids (Morpholinos), small interfering RNAs (siRNA) and transcription factors decoys of various chemistries. A detailed description of the different mechanisms of action of such oligonucleotide therapeutics can be found in the literature (e.g., Crooke in BBA (1999), 1489(1), 31-44; Tijsterman, et al. in Cell (2004), 117(1), 1-3; and Mann, et al. in J Clin Invest, (2000), 106(9), 1071-5).

The use of oligonucleotides for gene repair applications (see, e.g., Richardson, et al. in Stem Cells (2002), 20, 105-118) and micro RNAs are other examples from this rapidly growing field.

It is known in the art that nucleic acid therapeutics, irrespective of their actual chemical origin, may lack therapeutic efficacy owing to their instability in body fluids or because of inefficient uptake into cells, or both. Chemical modifications of such oligonucleotide, including the above-mentioned variants, as well as the formation of conjugates with ligands or polymers, represent one strategy to overcome such practical limitations.

A second set of strategies involves the use of carrier systems, in particular liposomes, for protecting, targeting and affording enhanced uptake into cells. Liposomes are artificial single, oligo or multilamellar vesicles having an aqueous core and being formed from amphiphilic molecules having both hydrophobic and hydrophilic components (amphiphiles). The cargo may be trapped in the core of the liposome, disposed in the membrane layer or at the membrane surface. Such carrier systems should meet an optimum score of the following criteria: high encapsulation efficiency and economical manufacture, colloidal stability, enhanced uptake into cells and of course low toxicity and immunogenicity.

Anionic or neutral liposomes are often excellent in terms of colloidal stability, as no aggregation occurs between the carrier and the environment. Consequently their biodistribution is excellent and the potential for irritation and cytotoxicity is low. However, such carriers lack encapsulation efficiency and do not provide an endosomolytic signal that facilitates further uptake into cells (Journal of Pharmacology and Experimental Therapeutics (2000), 292, 480-488 by Klimuk, et al.).

A great many of publications deal with cationic liposomal systems; see, e.g., Molecular Membrane Biology (1999), 16, 129-140 by Maurer, et al.; BBA (2000) 1464, 251-261 by Meidan, et al.; Reviews in Biology and Biotechnology (2001), 1(2), 27-33 by Fiset & Gounni. Although cationic systems provide high loading efficiencies, they lack colloidal stability, in particular after contact with body fluids. Ionic interactions with proteins and/or other biopolymers lead to in situ aggregate formation with the extracellular matrix or with cell surfaces. Cationic lipids have often been found to be toxic as shown by Filion, et al. in BBA (1997), 1329(2), 345-356; Dass in J. Pharm. Pharmacal. (2002), 54(5), 593-601; Hirko, et al. in Curr. Med. Chem., 10(14), 1185-1193.

These limitations were overcome by the addition of components that provide a steric stabilisation to the carriers. Polyethylenglycols of various chain length, for example, are known to eliminate aggregation problems associated with the use of cationic components in body fluids, and PEGylated cationic liposomes show enhanced circulation times in vivo (BBA (2001) 1510, 152-166 by Semple, et al.). However, the use of PEG does not solve the intrinsic toxicity problems associated with cationic lipids. It is also known that PEG substantially inhibits the productive entry of such liposomes into the cells or their intracellular delivery (Song, et al. in BBA (2002), 1558(1), 1-13). Quite recently, Morrissey, et al. (Nature Biotechnology (2005), 23 (8), 1002-1007) described a diffusible PEG-lipid for a cationic vector that is able to transfer siRNA into liver cells in vivo. However, the huge demand for such solutions and the given attrition rate of clinical development more than motivates the development of conceptually independent solutions.

Amphoteric liposomes represent a recently described class of liposomes having an anionic or neutral charge at pH 7.5 and a cationic charge at pH 4. WO 02/066490, WO 02/066012 and WO 03/070735, all to Panzner, et al. and incorporated herein by reference, give a detailed description of amphoteric liposomes and suitable lipids therefor. Further disclosures are made in WO 03/070220 and WO 03/070735, also to Panzner, et al. and incorporated herein by reference, which describe further pH sensitive lipids for the manufacture of such amphoteric liposomes.

Amphoteric liposomes have an excellent biodistribution and are very well tolerated in animals. They can encapsulate nucleic acid molecules with high efficiency.

The use of amphoteric liposomes as carriers for drugs for the prevention or treatment of different conditions or diseases in mammals requires stability of the liposomes after their injection into the bloodstream. For systemic applications especially, the drug must be stably encapsulated in the liposomes until eventual uptake in the target tissue or cells. The FDA's guidelines prescribe specific preclinical tests for drugs comprising liposomal formulations. For example, the ratio of encapsulated drug to free drug must be determined during the circulation time in the bloodstream.

After the injection of liposomes into the bloodstream, serum components interact with the liposomes and may lead to permeabilisation of the liposomal membrane. However, the release of a drug that is encapsulated by the liposome also depends upon the molecular dimensions of the drug. This means that a plasmid drug with a size of thousands of base pairs, for example, may be released much more slowly than smaller oligonucleotides or other small molecules. For liposomal delivery of drugs it is essential that the release of the drug during the circulation of the liposomes is as low as possible.

OBJECTS OF THE INVENTION

An object of the present invention therefore is to provide liposomes and mixtures of lipids capable of forming such liposomes having improved stability upon contact with human or animal serum.

In particular, an object of the present invention is to provide amphoteric liposomes having such improved serum stability.

Another object of the invention is to provide pharmaceutical compositions comprising such liposomes as a carrier for the targeted delivery of active agents or ingredients, including drugs such as nucleic acid drugs, e.g., oligonucleotides and plasmids.

A particular object of the present invention is to provide such a pharmaceutical composition for the treatment or prophylaxis of inflammatory, immune or autoimmune disorders of humans or non-human animals.

Yet another object of the present invention is to provide methods for the treatment of human or non-human animals in which a pharmaceutical composition comprising an active agent is targeted to a specific organ or organs, tumours or sites of infection or inflammation.

SUMMARY OF THE INVENTION

According to one aspect of the present invention therefore there is provided a mixture of lipids capable of encapsulating an active agent to form a liposome, said mixture comprising phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in a ratio of phosphatidylethanolamine to phosphatidylcholine in the range of about 0.5 to about 8.

Suitably, said ratio range from about 0.75 to about 5, preferably from about 1 to about 4.

In some embodiments, said phosphatidylcholine may be selected from DMPC, DPPC, DSPC, POPC or DOPC, or from phosphatidylcholines from natural sources such as, for example, soy bean PC and egg PC.

Said phosphatidylethanolamines may be selected from DOPE, DMPE and DPPE.

Preferred neutral lipids include DOPE, POPC, soy bean PC and egg PC.

It is known that cholesterol may stabilise phosphatidylcholine bilayers against serum attack. However, neither POPC nor DOPE form serum stable structures by themselves. It has now been found surprisingly that mixtures of DOPE and POPC may form serum stable liposomes.

Accordingly, in a particular aspect of the present invention, said mixture of lipids may be neutral. In some embodiments said mixture may consist or consist essentially of phosphatidylcholine and phosphatidylethanolamine in a ratio in the aforementioned range.

In another aspect of the present invention there are provided neutral liposomes comprising a mixture of lipids in accordance with the invention. Such liposomes may be used as a serum-stable excipient or carrier for active agents such as drugs.

In a different aspect of the present invention however, said mixture may further comprise one or more charged amphiphiles.

Preferably said one or more charged amphiphiles are amphoteric, being negatively charged or neutral at pH 7.4 and positively charged at pH 4.

By “amphoteric” herein is meant a substance, a mixture of substances or a supra-molecular complex (e.g., a liposome) comprising charged groups of both anionic and cationic character wherein:

-   -   (i) at least one of the charged groups has a pK between 4 and 8,     -   (ii) the cationic charge prevails at pH 4, and     -   (iii) the anionic charge prevails at pH 8,

resulting in an isoelectric point of neutral net charge between pH 4 and pH 8. Amphoteric character is by this definition different from zwitterionic character, as zwitterions do not have a pK in the range mentioned above. In consequence, zwitterions are essentially neutrally charged over a range of pH values; phosphatidylcholines and phosphatidylethanolamines are neutral lipids with zwitterionic character.

Suitably therefore, said mixture may comprise a plurality of charged amphiphiles which in combination with one another have amphoteric character. Preferably said one or more charged amphiphiles comprise a pH sensitive anionic lipid and a pH sensitive cationic lipid. Herein, such a combination of a chargeable cation and chargeable anion is referred to as an “amphoteric II” lipid pair. Said chargeable cation may have a pK value of between about 4 and about 8, preferably between about 5.0 or 5.5 and about 7.0 or 7.5. Said chargeable anion may have a pK value of between about 3.5 and about 7, preferably between about 4 or 4.5 and about 6.0 or 6.5. Examples include MoChol/CHEMS, DPIM/CHEMS and DPIM/DGSucc.

An “amphoteric lipid pair comprises a stable cation (e.g., DDAB/CHEMS, DOTAP/CHEMS and DOTAP/DOPS) and a chargeable anion, while an “amphoteric III” lipid pair comprises a stable anion and a chargeable cation (e.g., MoChol/DOPG and MoChol/Chol-SO₄).

It is of course possible within the scope of the present invention to use amphiphiles with multiple charges, such as, for example, amphipathic dicarboxylic acids, phosphatidic acid, amphipathic piperazine derivatives and the like. Such multi-charged amphiphiles may be pH sensitive amphiphiles or stable anions or cations, or they may have “mixed” character.

Suitably, said anionic lipid may be selected from DOGSucc, POGSucc, DMGSucc, DPGSucc and CHEMS.

Said cationic lipid may be selected from MoChol, HisChol and CHIM.

In yet another aspect of the present invention there are provided amphoteric liposomes comprising phosphatidylcholine and phosphatidylethanolamine in a ratio in the aforementioned range, a pH sensitive anionic lipid and a pH sensitive cationic lipid.

Said amphoteric liposomes may be negatively or neutrally charged at pH 7.4 and cationic at pH 4.

In another particular aspect of the present invention, said liposomes encapsulate at least one active agent. Said active agent may comprise a drug. In some embodiments said active agent may comprises a nucleic acid such as, for example, an oligonucleotide or DNA plasmid that is capable of being transcribed in a vertebrate cell into one or more RNAs, said RNAs being mRNAs, shRNAs, miRNAs or ribozymes, said mRNAs coding for one or more proteins or polypeptides.

Said oligonucleotide or other nucleic acid based drug may be encapsulated in said amphoteric liposomes. A substantial portion or all of said oligonucleotides may be physically entrapped in the amphoteric liposomes. The serum stable amphoteric liposomal formulations can be used for the intracellular delivery of drugs or for the prevention or treatment of a condition and/or disease in mammals or part of mammals, especially humans or their organs.

In some embodiments, said oligonucleotide may be adapted to target a nucleic acid encoding CD40, thereby to modulate expression of CD40 in mammalian cells. Suitably, said oligonucleotide may be directed against the mRNA of CD40.

In yet another aspect of the present invention there is provided a pharmaceutical composition comprising active agent-loaded amphoteric liposomes in accordance with the present invention and a pharmaceutically acceptable vehicle therefor.

Said composition may be formulated for high or low lipid doses, and suitably therefore the drug/lipid ratio may be adjusted to a desired lipid concentration. In some embodiments, said composition may further comprise empty liposomes to decrease said drug/lipid ratio, said empty liposomes having the same or similar size and composition to said active agent loaded liposomes. Said empty liposomes may comprise a mixture of lipids according to the present invention.

In yet another aspect, the present invention comprehends the use of a pharmaceutical composition according to the present invention for the prevention or treatment of an inflammatory, immune or autoimmune disorder of a human or non-human animal, wherein said composition comprises an oligonucleotide adapted to target a nucleic acid encoding CD40 for modulating the expression of CD40 in mammalian cells.

Said composition may be formulated for systemic or local administration. When used systemically, the present invention comprises the use of said composition inter alia for the prevention or treatment of graft rejection, graft-versus-host disease, diabetes type I, multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis, asthma, inflammatory bowel disease, psoriasis or thyroiditis.

When formulated for local application, the invention comprises the use of said composition inter alia for the prevention or treatment of graft rejection, graft-versus-host disease, inflammatory bowel disease, asthma, Crohn's disease or ulcerative colitis.

These and other embodiments are disclosed or are obvious from and encompassed by the following Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

The following Detailed Description, given by way of example, but not intended to limit the invention to specific embodiments described, may be understood in conjunction with the accompanying Figures, incorporated herein by reference, in which:

FIG. 1 is a graph of carboxyfluorescein (CF) release from the MoChol/CHEMS formulations of Table 1 (i.e., formulations comprising 100% DOPE (no POPC), DOPE/POPC ratios of 5, 3, 1.5, and 0.75, and 100% POPC (no DOPE)) below after incubation in full human serum for 4 hours. CF release is expressed as % of the unquenched CF signal. The x-axis shows the total amount of charged lipid at a 1:1 ratio between MoChol and CHEMS.

FIG. 2 is a graph of CF release from the MoChol/DMGSucc formulations of Table 4 (i.e., formulations comprising DOPE/POPC ratios of 3, 1.5, and 0.75) below after incubation in full human serum for 4 hours. CF release is expressed as % of the unquenched CF signal. The x-axis shows total amount of charged lipid at a 1:1 ratio between MoChol and DMGSucc.

FIG. 3 is graph of CF release from liposomes containing MoChol/CHEMS or MoChol/DMGSucc after incubation in full human serum at 37° C. CF release is expressed as % of the unquenched CF signal. Excess cation stabilises the liposomes against serum attack. DMGSucc is notably more stable then the CHEMS counterpart.

FIG. 4 is a graph of CF release from the MoChol/CHEMS and MoChol/DMGSucc formulations of Tables 3 and 6 below after incubation in full human serum at 37° C. The formulations have DOPE/POPC ratios of 2 and 4 and the ratio of cationic to anionic lipids is less than 1. Release is expressed as % of the unquenched CF signal.

FIG. 5 is a bar chart showing the biodistribution of the formulation POPC/DOPE/MoChol/CHEMS 15:45:20:20 having a size >150 nm when administered at low and high lipid doses in rat liver and spleen (see Example 7 below).

FIG. 6 is a bar chart showing the biodistribution of the formulation POPC/DOPE/MoChol/CHEMS 15:45:20:20 having a size <150 nm when administered at low and high lipid doses in rat liver and spleen (see Example 7 below).

FIG. 7 is a set of photographs of the limbs of sacrificed collagen-induced arthritic mice obtained by NIR-imaging and showing the biodistribution of amphoteric liposomes encapsulating Cy5.5 labelled CD40 antisense (see Example 8 below).

FIG. 8 is a graph showing the effect of treatment with amphoteric liposomes containing CD40 antisense on the paw swelling of inflamed mice.

FIG. 9 is a graph of the assessed clinical score of mice treated with amphoteric liposomes containing CD40 antisense.

FIG. 10 is a porcine CD40 cDNA sequence (SEQ ID NO:4) for targeting in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although a number of methods and materials similar or equivalent to those described herein can be used in the practice of the present invention, the preferred materials and methods are described herein.

As mentioned above, the amphoteric liposomes of the present invention may comprise anionic and cationic components, wherein both components are pH-sensitive, as disclosed in WO 02/066012, the contents of which are incorporated herein by reference.

Cationic lipids that are sensitive to pH are disclosed in WO 02/066489 and WO 03/070220, and in the references made therein, in particular Budker, et al. 1996, Nat Biotechnol. 14(6):760-4, the contents of all of which are incorporated herein by reference.

Preferred cationic components are MoChol, HisChol and CHIM, especially MoChol.

Preferred anionic lipids are selected from the group comprising: DOGSucc, POGSucc, DMGSucc, DPGSucc and CHEMS, especially DOGSucc, DMGSucc and CHEMS.

The following abbreviations for lipids are used herein, the majority of which abbreviations are in standard use in the literature:

-   -   PC Phosphatidylcholine, unspecified membrane anchor     -   PE Phosphatidylethanolamine, unspecified membrane anchor     -   DMPC Dimyristoylphosphatidylcholine     -   DPPC Dipalmitoylphosphatidylcholine     -   DSPC Distearoylphosphatidylcholine     -   POPC Palmitoyl-oleoylphosphatidylcholine     -   DOPC Dioleoylphosphatidylcholine     -   DOPE Dioleoylphosphatidylethanolamine     -   DMPE Dimyristoylphosphatidylethanolamine     -   DPPE Dipalmitoylphosphatidylethanolamine     -   CHEMS Cholesterolhemisuccinate     -   CHIM Cholesterol-(3-imidazol-1-yl propyl)carbamate     -   DDAB Dimethyldioctadecylammonium bromide     -   DOTAP (1,2-dioleoyloxypropyl)-N,N,N-trimethylammonium salt     -   DOPS Dioleoylphosphatidylserine     -   DOPG Dioleoylphosphatidylglycerol     -   Chol-SO₄ cholesterol sulfate     -   MoChol 4-(2-Aminoethyl)-Morpholino-Cholesterolhemisuccinate:

-   -   HisChol Histaminyl-Cholesterolhemisuccinate:

-   -   DGSucc 1,2-Dipalmitoyglycerol-3-hemisuccinate (& Distearoyl-,         dimyristoyl-Dioleoyl or palmitoyl-oleoylderivatives) (in the         structure below the acyl chain is shown schematically)

It has been found that the ratio between the cationic and anionic lipids (the charge ratio) not only determines the isoelectric point, but may also affect the serum stability of the composition. Accordingly, said charge ratio may vary from 4:1 to 1:4, preferably between 3:1 and 1:3 (cation:anion).

In some embodiments of the invention, the cation may be present in excess over the anion. Preferably said charge ratio is between 3:1 and 2:1. The total amount of charged lipids may vary from 5 to 95 mol. % of the lipid mixture, preferably from 30 to 80 mol. %, and more preferably from 45 or 50 mol. % to 75 mol. %, with the remaining lipids being formed from the neutral phospholipids PC and PE.

Alternatively, the cation and anion may be present in substantially equal amounts. The total amount of charged lipids may vary from 5 to 75 mol. % of the lipid mixture, preferably from 20 to 65 mol. %, with the remaining lipids being formed from the neutral phospholipids PC and PE.

In another alternative, the anion may be present in excess over the cation. Said charge ratio may be between 1:3 and 1:2, preferably about 1:2 (cation:anion). The total amount of charged lipids may vary from 40 mol. % to 75 or 80 mol. % of the lipid mixture, preferably from 45 or 50 mol. % to 70 or 75 mol. %, with the remaining lipids being formed from the neutral phospholipids PC and PE.

A number of different combinations of cations and anions may be selected from the lists of suitable components given above. Advantageously, the invention may be practised using MoChol or CHIM as a chargeable cation and CHEMS, DMGSucc or DOGSucc as a chargeable anion.

Presently preferred liposomes are made from a mixture of lipids comprising POPC and DOPE in a ratio between 1:1 and 1:4 and an amphoteric lipid pair selected from MoChol and CHEMS, MoChol and DMGSucc, MoChol and DOGSucc, CHIM and CHEMS, and CHIM and DMGSucc, in a ratio between 3:1 and 1:1, wherein the amount of charged lipids is between 30 and 80 mol. % of the lipid mixture.

Specific examples of such liposomes in accordance with the present invention include, but are not limited to:

POPC/DOPE/MoChol/CHEMS 6:24:53:17 POPC/DOPE/MoChol/CHEMS 6:24:47:23 POPC/DOPE/MoChol/CHEMS 15:45:20:20 POPC/DOPE/MoChol/CHEMS 10:30:30:30 POPC/DOPE/MoChol/CHEMS 24.5:35.5:20:20 POPC/DOPE/MoChol/CHEMS 16:24:30:30 POPC/DOPE/MoChol/DMGSucc 6:24:53:17 POPC/DOPE/MoChol/DMGSucc 6:24:47:23 POPC/DOPE/MoChol/DMGSucc 15:45:20:20 POPC/DOPE/MoChol/DMGSucc 10:30:30:30 POPC/DOPE/MoChol/DMGSucc 24.5:35.5:20:20 POPC/DOPE/MoChol/DMGSucc 16:24:30:30 POPC/DOPE/MoChol/DOGSucc 12.5:37.5:33:17 POPC/DOPE/MoChol/DOGSucc 7.5:22.5:47:23 POPC/DOPE/CHIM/CHEMS 12.5:37.5:33:17 POPC/DOPE/CHIM/CHEMS 7.5:22.5:47:23 POPC/DOPE/CHIM/DMGSucc 12.5:37.5:33:17 POPC/DOPE/CHIM/DMGSucc 7.5:22.5:47:23

Further presently preferred liposomes comprise a mixture of lipids comprising POPC and DOPE in a ratio between 1:1 and 1:4, DMGSucc or DOGSucc, and MoChol, wherein the molar amount of DMGSucc or DOGSucc exceeds the molar amount of MoChol and the amount of charged lipids is between 30 and 80 mol. %. Preferably, the charge ratio is between 1:2 and 1:3 and charged components constitute between 45 or 50 mol. % and 70 or 75 mol. % of the lipid mixture.

Specific examples of such further liposomes include, but are not limited to:

POPC/DOPE/MoChol/DMGSucc 6:24:23:47 POPC/DOPE/MoChol/DMGSucc 8:32:20:40 POPC/DOPE/MoChol/DMGSucc 10:40:17:33 POPC/DOPE/MoChol/DMG Succ 10:20:23:47 POPC/DOPE/MoChol/DMGSucc 13:27:20:40 POPC/DOPE/MoChol/DMGSucc 10:30:20:40 POPC/DOPE/MoChol/DMGSucc 17:33:17:33 POPC/DOPE/MoChol/DOGSucc 12.5:37.5:17:33

Without being limited to such use, the materials described in the present invention are well suited for use as carriers for nucleic acid-based drugs such as for example oligonucleotides and DNA plasmids. These drugs are classified into nucleic acids that encode one or more specific sequences for proteins, polypeptides or RNAs and into oligonucleotides that can specifically regulate protein expression levels or affect the protein structure through inter alia interference with splicing and artificial truncation.

In some embodiments of the present invention, therefore, the nucleic acid-based therapeutic may comprise a nucleic acid that is capable of being transcribed in a vertebrate cell into one or more RNAs, which RNAs may be mRNAs, shRNAs, miRNAs or ribozymes, wherein such mRNAs code for one or more proteins or polypeptides. Such nucleic acid therapeutics may be circular DNA plasmids, linear DNA constructs, like MIDGE vectors (Minimalistic Immunogenically Defined Gene Expression) as disclosed in WO 98/21322 or DE 19753182, or mRNAs ready for translation (e.g., EP 1392341).

In another embodiment of the invention, oligonucleotides may be used that can target existing intracellular nucleic acids or proteins. Said nucleic acids may code for a specific gene, such that said oligonucleotide is adapted to attenuate or modulate transcription, modify the processing of the transcript or otherwise interfere with the expression of the protein. The term “target nucleic acid” encompasses DNA encoding a specific gene, as well as all RNAs derived from such DNA, being pre-mRNA or mRNA. A specific hybridisation between the target nucleic acid and one or more oligonucleotides directed against such sequences may result in an inhibition or modulation of protein expression. To achieve such specific targeting, the oligonucleotide should suitably comprise a continuous stretch of nucleotides that is substantially complementary to the sequence of the target nucleic acid.

Oligonucleotides fulfilling the abovementioned criteria may be built with a number of different chemistries and topologies. Oligonucleotides may be single stranded or double stranded.

The mechanisms of action of oligonucleotides may vary and might comprise effects on inter alfa splicing, transcription, nuclear-cytoplasmic transport and translation.

In a preferred embodiment of the invention single stranded oligonucleotides may be used, including, but not limited to, DNA-based oligonucleotides, locked nucleic acids, 2′-modified oligonucleotides and others, commonly known as antisense oligonucleotides. Backbone or base or sugar modifications may include, but are not limited to, Phosphothioate DNA (PTO), 2′O-methyl RNA (2′Ome), 2′ O-methoxyethyl-RNA (2′MOE), peptide nucleic acids (PNA), N3′-P5′ phosphoamidates (NP), 2′fluoroarabino nucleic acids (FANA), locked nucleic acids (LNA), Morpholine phosphoamidate (Morpholino), Cyclohexene nucleic acid (CeNA), tricyclo-DNA (tcDNA) and others. Moreover, mixed chemistries are known in the art, being constructed from more than a single nucleotide species as copolymers, block-copolymers or gapmers or in other arrangements. In addition to the aforementioned oligonucleotides, protein expression can also be inhibited using double stranded RNA molecules containing the complementary sequence motifs. Such RNA molecules are known as siRNA molecules in the art (e.g., WO 99/32619 or WO 02/055693). Again, various chemistries were adapted to this class of oligonucleotides. Also, DNA/RNA hybrid systems are known in the art.

In another embodiment of the present invention, decoy oligonucleotides can be used. These double stranded DNA molecules and chemical modifications thereof do not target nucleic acids but transcription factors. This means that decoy oligonucleotides bind sequence-specific DNA-binding proteins and interfere with the transcription (e.g. Cho-Chung, et al. in Curr. Opin. Mol. Ther., 1999).

In a further embodiment of the invention, oligonucleotides that may influence transcription by hybridizing under physiological conditions to the promoter region of a gene may be used. Again various chemistries may adapt to this class of oligonucleotides.

In a still further alternative of the invention, DNAzymes may be used. DNAzymes are single-stranded oligonucleotides and chemical modifications thereof with enzymatic activity. Typical DNAzymes, known as the “10-23” model, are capable of cleaving single stranded RNA at specific sites under physiological conditions. The 10-23 model of DNAzymes has a catalytic domain of 15 highly conserved deoxyribonucleotides, flanked by 2 substrate-recognition domains complementary to a target sequence on the RNA. Cleavage of the target mRNAs may result in their destruction and the DNAzymes recycle and cleave multiple substrates.

In yet another embodiment of the invention, ribozymes can be used. Ribozymes are single stranded oligoribonucleotides and chemical modifications thereof with enzymatic activity. They can be operationally divided into two components, a conserved stem-loop structure forming the catalytic core and flanking sequences which are reverse complementary to sequences surrounding the target site in a given RNA transcript. Flanking sequences may confer specificity and may generally constitute 14-16 nt in total, extending on both sides of the target site selected.

In a still further embodiment of the invention, aptamers may be used to target proteins. Aptamers are macromolecules composed of nucleic acids, such as RNA or DNA, and chemical modifications thereof that bind tightly to a specific molecular target and are typically 15-60 nt long. The chain of nucleotides may form intramolecular interactions that fold the molecule into a complex three-dimensional shape. The shape of the aptamer allows it to bind tightly against the surface of its target molecule including but not limited to acidic proteins, basic proteins, membrane proteins, transcription factors and enzymes. Binding of aptamer molecules may influence the function of a target molecule.

All of the above-mentioned oligonucleotides may vary in length between as little as 10, preferably 15 and even more preferably 18, and 50, preferably 30 and more preferably 25, nucleotides. The fit between the oligonucleotide and the target sequence is preferably perfect with each base of the oligonucleotide forming a base pair with its complementary base on the target nucleic acid over a continuous stretch of the abovementioned number of oligonucleotides. The pair of sequences may contain one or more mismatches within the said continuous stretch of base pairs, although this is less preferred. In general, the type and chemical composition of such nucleic acids is of little impact for the performance of the inventive liposomes as vehicles be it in vivo or in vitro, and the skilled artisan may find other types of oligonucleotides or nucleic acids suitable for combination with the inventive liposomes.

In a preferred embodiment of the invention however, oligonucleotides may used that are adapted to target a nucleic acid encoding the CD40 gene, its sense or antisense strand, any exons or introns or untranslated regions thereof, thereby to modulate expression of CD40 in mammalian cells.

In another preferred embodiment of the invention, said oligonucleotides may directed against any mRNA of CD40, wherein such mRNAs include pre-mRNA and their subsequently matured forms.

Protein expression can be specifically down-regulated using oligonucleotides such, for example, as antisense, locked nucleic acids (LNA), peptide nucleic acids (PNA), morpholino nucleic acids (Morpholinos) and small interfering RNAs (siRNA) of various chemistries.

CD40 was first described by Pauli, et al. 1984 (Cancer Immunol. Immunotherapy 17: 173-179). The protein is primarily expressed on dendritic cells, endothelial cells and B-cells and interacts with its ligand (CD40 ligand or CD154) on T-cells. The signalling between CD40 and CD154 is crucial for the development of a humoral immune response. Over-stimulation of the pathway may lead to a variety of immune-associated disorders, including graft rejection, graft-versus-host disease, multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis, asthma, inflammatory bowel disease, psoriasis and thyroiditis. CD40 over-expression might also be involved in tumour growth (Gruss, et al. 1997, Leuk. Lymphoma. 24(5-6): 393-422) and enhanced levels of a soluble form of CD40 were reported to be associated with Alzheimers disease (Mocali et al. 2004, Exp Gerontol. 39(10):1555-61. CD40 signals into the NF-κB pathway, consequently leading to activation of the transcription factor and the eventual release of cytokines such as IL-1, TNFα and IFNγ, which in turn activate other cells, thus promoting inflammation using a positive feedback mechanism.

Inhibition of the early events in the pathway described above has been proposed as an effective strategy to inhibit immune disorders or inflammation processes. Examples include the competitive binding of TNFα using antibodies, receptor blocking using antibodies against the TNFα-receptor and competitive inhibition of NF-κB binding. Since CD40 signals through its interaction with the trimeric ligand, CD154, inhibition of the signalling event with small molecule inhibitors is unlikely and therapeutic developments have therefore focused on the use of blocking antibodies. More specifically, the CD40/CD154 interaction may be blocked using antibodies targeted against one of the components, as described by Holstager, et al. 2000 (J. Biol. Chem. 275:15392-15398) or Baccam & Bishop 1999 (Eur. J. Immunol. 29: 3855-3866). However, the CD40 antibodies under development give rise to side reactions, and there is therefore a need for alternative means to cut the inflammatory feedback loop at this point.

A number of oligonucleotide sequences targeted against CD40 mRNA have been validated in vitro so far. US 2004/0186071 and U.S. Pat. No. 6,197,584, both to Bennett, et al., for example, give a detailed description of such oligonucleotides based on antisense mechanisms. Pluvinet, et al. in Blood, 2004 first described the down-regulation of CD40 using siRNA against the human target. Further, WO 2004/090108 to Manoharan describes the applicability of novel oligonucleotides to inhibit the expression of CD40 protein. Indirect means to down-regulate the CD40 expression are described in DE 10049549 to Hecker and Wagner, using the inhibition of transcription factor IFR-1. Suitable specific nucleic acids for modulating the expression of CD40 are set forth in Example 11 below.

In a particular aspect of the present invention therefore there is provided a pharmaceutical composition comprising an oligonucleotide directed against CD40 as an active agent and an amphoteric liposome of the present invention as an excipient. Such formulations have been found to be therapeutically active in the treatment of inflammations and autoimmune disorders, and accordingly the invention further comprehends the use of the composition of the invention for the prevention or treatment of inflammations, immune or autoimmune disorders, including graft rejection, graft-versus-host disease, multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis, asthma, asthma bronchiale, inflammatory bowel disease, psoriasis, thyroiditis, Morbus Crohn, Colitis ulcerosa, COPD and atopic dermatitis.

The pharmaceutical composition of the present invention may also be used for topical treatments, for example the treatment of inflamed mucosa. In particular, the composition of the invention may be used for the treatment or prophylaxis of inflammatory bowel disease or graft rejection. The composition of the present invention may also be adapted for topical application to the skin or lungs.

Liposomes have been widely used to alter the pharmacokinetic and biodistribution profile of encapsulated drugs in vivo. The liposomes of the present invention, together with their cargo, may be cleared rapidly and to a great extent by the liver. However, the pharmacokinetic parameters as well as the biodistribution pattern may be controlled by adjusting the size of the liposomes and/or the lipid dose as illustrated in the examples below.

In some embodiments, the liposomes of the present invention may have a size greater than about 150 nm. Such liposomes may be administered at a low lipid dose. Said liposomes may be unilamellar, oligolamellar or multilamellar. Such a dosing scheme allows for effective and rapid targeting to the liver and avoids the accumulation of liposomes and drug in other organs, such as the spleen.

Alternatively, such liposomes having a size greater than about 150 nm may be administered at a high lipid dose, leading to saturation of the liver and an alteration of the biodistribution pattern to an accumulation of the liposomes in the spleen and more distal sites in the circulation, such as sites of infection or inflammation or tumours. These areas of the body have fenestrated or incomplete capillaries through which liposomes may be filtered out. Furthermore, it is known that the spleen and such other areas of infection or inflammation and many tumors often have high contents of macrophages which can remove the liposomes from the circulation.

Said pharmaceutical composition according to the present invention may be provided with a high lipid dose by different methods. In some embodiments, the drug/lipid ratio of the composition can be lowered to achieve the desired lipid concentration. Alternatively, the lipid concentration of the pharmaceutical composition may be controlled by adding empty liposomes of comparable composition and size to the drug loaded liposomes.

In some embodiments, the liposomes according to the present invention may have a size of less than about 150 nm. Said liposomes may be unilamellar, oligolamellar or multilamellar. The spleen acts as a filter which removes unwanted red blood cells and particles from the blood. Large liposomes are also retained by the reticular filter in the same way. However, small liposomes may escape and thus do not accumulate in spleen. Accordingly, liposomes according to the present invention, having a size of less than 150 nm may circumvent the spleen as an organ.

Such liposomes having a size of less than 150 nm may be administered at a low lipid dose in order to target liver cells. Such liposomes are particularly well adapted to penetrate fully the entire liver and to reach a substantial portion of the parenchymal cells of the liver such as hepatocytes.

Alternatively, said liposomes having a size of less than 150 nm may be administered at a high lipid dose to target more distal sites in the circulation, such as areas of infection or inflammation or solid tumours, and simultaneously to circumvent the spleen.

In general, the pharmacokinetic profile and the biodistribution of the liposomes of the present invention may depend upon many factors. Next to the lipid composition of the liposomes, the size and lipid dose determine the in vivo fate of the liposomes. The liposomes of the invention may be unilamellar, oligolamellar or multilamellar, irrespective of their size.

In some embodiments, the liposomes of the present invention may be used to target an inflamed lung by systemic administration to a human or non-human animal patient.

Starting from the data presented herein, those skilled in the art will be able to establish appropriate dosage regimens for other species, in particular for other mammals or humans. Specifically, whether a lipid dose in another species (e.g. human) is “low” or “high” can be determined by pharmacokinetic data. The pharmacokinetic of liposomes follows a two compartment model. As mentioned above, high lipid doses lead to a saturation of the liver and an alteration of the biodistribution pattern. This leads to enhanced Cmax values in the terminal part of the pharmacokinetic curve.

The pharmaceutical composition of the present invention may be formulated for use as a colloid in a suitable pharmacologically acceptable vehicle. Vehicles such as water, saline, phosphate buffered saline and the like are well known to those skilled in the art for this purpose.

In some embodiments, the composition of the present invention may be administered at a physiological pH of between about 7 and about 8. To this end, the composition comprising the active agent, excipient and vehicle may be formulated to have a pH in this range.

Methods for manufacturing liposomes are known to those skilled in the art. They include, but are not limited to, extrusion through membranes of defined pore size, injection of lipid solutions in ethanol into the water phase containing cargo or high pressure homogenisation.

Also, it is known in the art that nucleic acid therapeutics can be contacted with the lipids at neutral pH, resulting in volume inclusion of a certain percentage of the solution containing the nucleic acid. High concentrations of lipids ranging from 50 mM to 150 mM are preferred to achieve substantial encapsulation of the drug.

In contrast to such standard procedures, amphoteric liposomes offer the distinct advantage of binding nucleic acids at or below their isoelectric point, thereby concentrating the drug at the liposome surface. Such a process is described in WO 02/066012 in more detail. Upon elevating the pH of the liposomes to physiological pH (about pH 7.4) the negatively charged nucleic acids dissociate from the liposomal membrane. Irrespective of the actual production process, the non-encapsulated active drug can be removed from the liposomes after the initial production step, wherein liposomes are formed as tight containers. Again, the technical literature and the references included here describe such methodology in detail and suitable process steps may include, but are not limited to, size exclusion chromatography, sedimentation, dialysis, ultrafiltration, diafiltration and the like.

In some embodiments of the invention, more than 80 wt. % of the drug may be disposed inside said liposomes.

However, such removal of non-encapsulated material is not mandatory and in some embodiments the composition may comprises entrapped as well as free drug.

The particle size of the liposomes may be between 50 and 500 nm, preferably between 50 and 300 nm.

Following is a description by way of example only with reference to the accompanying drawings of embodiments of the present invention.

EXAMPLES Example 1 Preparation of carboxyfluorescein (CF) Loaded Liposomes with the Amphoteric H Lipids MoChol and CHEMS

Stock solutions of lipids in chloroform were mixed and finally evaporated in a round bottom flask to dryness under vacuum. Lipid films were hydrated with 100 mM CF in PBS pH 7.5. The resulting lipid concentration was 20 mM. The suspensions were hydrated for 45 minutes in a water bath at room temperature, sonicated for 5 minutes following by three freeze/thaw cycles at −70° C. After thawing the liposomal suspensions were extruded 15 times through polycarbonate membranes with a pore size of 100 nm. Non-encapsulated CF was removed by gel filtration, whereas the liposomes were diluted by a factor of three. Lipid recovery and concentration was analysed by organic phosphate assay. Particle size was measured by dynamic light scattering on a Malvern Zetasizer 3000 HSA.

TABLE 1 Variation of the ratio DOPE/POPC and the total amount of charged components Lipids Composition DOPE/MoChol/CHEMS 60:20:20 DOPE/MoChol/CHEMS 50:20:30 DOPE/MoChol/CHEMS 40:30:30 DOPE/MoChol/CHEMS 20:40:40 POPC/MoChol/CHEMS 60:20:20 POPC/MoChol/CHEMS 40:30:30 POPC/MoChol/CHEMS 20:40:40 POPC 100 POPC/DOPE 20:80 POPC/DOPE/MoChol/CHEMS 10:50:20:20 POPC/DOPE/MoChol/CHEMS 7:35:30:30 POPC/DOPE/MoChol/CHEMS 3:17:40:40 POPC/DOPE 25:75 POPC/DOPE/MoChol/CHEMS 15:45:20:20 POPC/DOPE/MoChol/CHEMS 10:30:30:30 POPC/DOPE/MoChol/CHEMS 5:15:40:40 POPC/DOPE 40:60 POPC/DOPE/MoChol/CHEMS 24.5:35.5:20:20 POPC/DOPE/MoChol/CHEMS 16:24:30:30 POPC/DOPE/MoChol/CHEMS 8:12:40:40 POPC/DOPE 57:43 POPC/DOPE/MoChol/CHEMS 34:26:20:20 POPC/DOPE/MoChol/CHEMS 22.8:17.2:30:30 POPC/DOPE/MoChol/CHEMS 11.4:8.6:40:40

TABLE 2 Variation of the ratio MoChol/CHEMS Lipids Composition POPC/DOPE/MoChol/CHEMS 6:24:53:17 POPC/DOPE/MoChol/CHEMS 6:24:47:23 POPC/DOPE/MoChol/CHEMS 6:24:35:35 POPC/DOPE/MoChol/CHEMS 6:24:23:47

TABLE 3 Variation of ratio DOPE/POPC and the total amount of charged components Lipids Composition POPC/DOPE/MoChol/CHEMS 4:16:27:53 POPC/DOPE/MoChol/CHEMS 6:24:23:47 POPC/DOPE/MoChol/CHEMS 8:32:20:40 POPC/DOPE/MoChol/CHEMS 10:40:17:33 POPC/DOPE/MoChol/CHEMS 7:13:27:53 POPC/DOPE/MoChol/CHEMS 10:20:23:47 POPC/DOPE/MoChol/CHEMS 13:26:20:40 POPC/DOPE/MoChol/CHEMS 17:33:17:33

Example 2 Preparation of carboxyfluorescein (CF) Loaded Liposomes with the Amphoteric II Lipids MoChol and DMGSucc

Liposomes were prepared as described in Example 1.

TABLE 4 Variation of the ratio DOPE/POPC and the total amount of charged components Lipids Composition POPC/DOPE/MoChol/DMGSucc 15:45:20:20 POPC/DOPE/MoChol/DMGSucc 10:30:30:30 POPC/DOPE/MoChol/DMGSucc 5:15:40:40 POPC/DOPE/MoChol/DMGSucc 24.5:35.5:20:20 POPC/DOPE/MoChol/DMGSucc 16:24:30:30 POPC/DOPE/MoChol/DMGSucc 8:12:40:40 POPC/DOPE/MoChol/DMGSucc 34:26:20:20 POPC/DOPE/MoChol/DMGSucc 22.8:17.2:30:30 POPC/DOPE/MoChol/DMGSucc 11.4:8.6:40:40

TABLE 5 Variation of the ratio MoChol/DMGSucc Lipids Composition POPC/DOPE/MoChol/DMGSucc 6:24:53:17 POPC/DOPE/MoChol/DMGSucc 6:24:47:23 POPC/DOPE/MoChol/DMGSucc 6:24:35:35 POPC/DOPE/MoChol/DMGSucc 6:24:23:47

TABLE 6 Variation of ratio DOPE/POPC and the total amount of charged components Lipids Composition POPC/DOPE/MoChol/DMGSucc 4:16:27:53 POPC/DOPE/MoChol/DMGSucc 6:24:23:47 POPC/DOPE/MoChol/DMGSucc 8:32:20:40 POPC/DOPE/MoChol/DMGSucc 10:40:17:33 POPC/DOPE/MoChol/DMGSucc 7:13:27:53 POPC/DOPE/MoChol/DMGSucc 10:20:23:47 POPC/DOPE/MoChol/DMGSucc 13:26:20:40 POPC/DOPE/MoChol/DMGSucc 17:33:17:33

Example 3 Preparation of carboxyfluorescein (CF) Loaded Liposomes with the Amphoteric II Lipids MoChol and DOGSucc

Liposomes were prepared as described in Example 1.

TABLE 7 Variation of the ratio MoChol/DOGSucc and the total amount of charged components Lipids Composition Serum Stability POPC/DOPE/MoChol/DOGSucc 12.5:37.5:17:33 + POPC/DOPE/MoChol/DOGSucc 12.5:37.5:33:17 + POPC/DOPE/MoChol/DOGSucc 7.5:22.5:23:47 − POPC/DOPE/MoChol/DOGSucc 7.5:22.5:47:23 +

Example 4 Preparation of carboxyfluorescein (CF) Loaded Liposomes with the Amphoteric II Lipids CHIM and CHEMS

Liposomes were prepared as described in Example 1.

TABLE 8 Variation of the ratio CHIM/CHEMS and the total amount of charged components Serum Lipids Composition Stability POPC/DOPE/CHIM/CHEMS 12.5:37.5:17:33 − POPC/DOPE/CHIM/CHEMS 12.5:37.5:33:17 + POPC/DOPE/CHIM/CHEMS 7.5:22.5:23:47 − POPC/DOPE/CHIM/CHEMS 7.5:22.5:47:23 +

Example 5 Preparation of carboxyfluorescein (CF) Loaded Liposomes with the Amphoteric II Lipids CHIM and DMGSucc

Liposomes were prepared as described in Example 1.

TABLE 9 Variation of the ratio CHIM/DMGSucc and the total amount of charged components Lipids Composition Serum Stability POPC/DOPE/CHIM/DMGSucc 12.5:37.5:17:33 − POPC/DOPE/CHIM/DMGSucc 12.5:37.5:33:17 + POPC/DOPE/CHIM/DMGSucc 7.5:22.5:23:47 − POPC/DOPE/CHIM/DMGSucc 7.5:22.5:47:23 +

Example 6 Serum Stability Test of CF-Loaded Amphoteric Liposomes of Examples 1 and 2

Carboxyfluorescein (CF) was used as model drug to determine the serum stability of amphoteric liposomes. As well as oligonucleotides, CF is negatively charged.

25 μl of the CF-loaded liposomes were mixed with 100 μl pre-warmed full human serum or PBS, respectively and incubated at 37° C. At defined time points 5 μl sample was transferred into a 96-well microliter plate to 20 μl PBS, pH 7.5 or 20 μl 20% Triton X-100. Finally 275 μl PBS were added to each well and fluorescence intensity was measured at 475/530 nm.

The serum stability was observed over a period of 4 hours by determining the release of CF from the liposomes via the fluorescence measurement. The released amount of CF (in %) is measured at defined time points as well as after a treatment of the liposomes with a detergent (Triton X-100) to get a 100% release value.

Results:

Mixtures of POPC and DOPE are stable in serum. POPC itself does not form liposomes that withstand attack from serum. In addition, DOPE does not form liposomes at all. Quite surprisingly, mixtures from both components were found to be very stable and resistant against serum attack. In this example, DOPE/POPC ratios from 0.75 to 5 were found to form stable structures with a broad optimum between 1.5 and 5 (see also FIGS. 1 and 2).

Charged components and neutral lipids are independent variables. Serum sensitivity for a 1:1 ratio of both MoChol/CHEMS or MoChol/DMGSucc is low to very low and stable particles are formed over a wide range of mixtures. At least 60 or 70 mol. % of total charged components was required to affect significantly the bilayer stability.

The serum stability of lipid mixtures containing 70% of charged components (see Tables 2 and 5) is shown in FIG. 3. In general, an excess of MoChol has a stabilising effect.

The formulations of Tables 3 and 6 that were tested for serum stability have DOPE and POPC in a ratio of either 2:1 or 4:1. The total amount of the charged lipids was titrated from 80% down to 50%. The results are shown in FIG. 4.

Example 7 Biodistribution of Serum Stable Amphoteric Liposomes

Stock solutions of lipids (+/−1% 14C-DPPC) in chloroform were mixed and finally evaporated in a round bottom flask to dryness under vacuum. Lipid films were hydrated with 1.5 ml 3H-Inulin in PBS pH 7.5 or 5 ml PBS alone. The resulting lipid concentration was 100 mM. The suspensions were hydrated for 45 minutes in a water bath at room temperature, sonicated for 30 minutes following by three freeze/thaw cycles at −70° C. After thawing the liposomal suspensions were extruded 15 times through polycarbonate membranes with an appropriate pore size. Liposomes were separated from non-encapsulated 3H-Inulin by ultracentrifugation (twice).

Lipid recovery and concentration was analysed by organic phosphate assay and in case of radiolabelled particles, the encapsulation efficiency was measured by liquid scintillation. Particle size was measured by dynamic light scattering on a Malvern Zetasizer 3000 HSA. The resulting unlabelled and radiolabelled preparations were mixed up and diluted with PBS to the final lipid concentrations.

Formulations:

Size Lipid 3H 14C Number Formulation [nm] [mM] [kBq/ml] [kBq/ml] LD-1 POPC/DOPE/MoChol/ 229 12.3 332 52 CHEMS 15:45:20:20 HD-2 POPC/DOPE/MoChol/ 231 54.8 453 70 CHEMS 15:45:20:20 LD-3 POPC/DOPE/MoChol/ 148 10 173 53 CHEMS 15:45:20:20 HD-4 POPC/DOPE/MoChol/ 140 50 182 58 CHEMS 15:45:20:20

Biodistribution Study

39 male Wistar rats (Charles River) were divided into five groups and injected intravenously via the tail vein. At specific time points blood samples (for PK) and/or tissue samples (for BD) were collected and analysed by catalytic oxidation under high temperature. Percentage of carry over between samples was determined and included into the analysis of the data set.

Study group Formulation Number Animals 1 POPC/DOPE/MoChol/CHEMS LD-1 9 15:45:20:20 2 POPC/DOPE/MoChol/CHEMS HD-2 9 15:45:20:20 3 POPC/DOPE/MoChol/CHEMS LD-3 9 15:45:20:20 4 POPC/DOPE/MoChol/CHEMS HD-4 9 15:45:20:20 5 PBS PBS 3

The results of the biodistribution study are shown in FIGS. 5-6 wherein biodistribution of the different liposomal formulations in liver and spleen is shown. The accumulation of the liposomes in other organs did not exceed 5% and is therefore not shown. FIG. 5 clearly demonstrates that amphoteric liposomes of the present invention having a size >150 nm accumulate solely in the liver when administered in low lipid doses. In contrast, by administering the same liposomal formulation in a high lipid dose it could be shown that the biodistribution pattern is changed. Next to the liver the liposomes with a size >150 nm accumulate in spleen as well.

FIG. 6 shows the biodistribution of amphoteric liposomes of the present invention prepared in a size <150 nm. Whereas the biodistribution of these liposomes administered at low lipid dose does not differ from the liposomes with a size >150 nm, it can be demonstrated that an administration of the liposomes having a size <150 nm in high lipid dose does not lead to an accumulation in spleen.

Example 8 Biodistribution of Amphoteric Liposomes Encapsulating Cy5.5 Labelled CD40 Antisense in Collagen Induced Arthritic Mice

Stock solutions of lipids in chloroform were mixed and finally evaporated in a round bottom flask to dryness under vacuum. Lipid film was hydrated with Cy5.5 labelled CD40 antisense in 10 mM NaAc, 50 mM NaCl, pH 4.5. The resulting lipid concentration was 20 mM. The suspensions were hydrated for 45 minutes in a water bath at 50° C., sonicated for 5 minutes following by a freeze/thaw cycle at −70° C. After thawing the liposomal suspensions were extruded 19 times through 200 nm polycarbonate membranes. After the extrusion process the pH of the liposomal suspension was shifted to pH 7.5 by adding 1/10 Vol. 1M HEPES, pH 8. Non-encapsulated Cy5.5 labelled CD40 antisense was removed by high speed sedimentation (twice) and discarding the supernatant.

Lipid recovery and concentration was analysed by organic phosphate assay. Encapsulation efficiency was measured by fluorescence spectroscopy. Particle size was measured by dynamic light scattering on a Malvern Zetasizer 3000 HSA.

Empty liposomes were produced by injecting 10 Vol-% of an ethanolic lipid solution (a mixture of 15 mol. % POPC, 45 mol. % DOPE, 20 mol. % MoChol and 20 mol. % CHEMS) into 10 mM NaAc 50 mM NaCl pH 4.5. The resulting lipid concentration was 2 mM. The pH of this solution was immediately shifted with 1/10 volume 1M Hepes pH 8. To concentrate the diluted liposomes the suspension was diafiltered.

Encap- Size Lipid sulation Formulation [nm] [mM] Cargo efficiency POPC/DOPE/MoChol/CHEMS 192 19 Cy5.5 77% 15:45:20:20 OCD40-DN POPC/DOPE/MoChol/CHEMS 104 195 empty — 15:45:20:20

For the biodistribution study in mice the filled and empty liposomes were mixed as follows:

200 μl Cy5.5 liposomes and 41 μl empty liposomes

DBA/1 mice were immunized by subcutaneous injections of type II collagen (200 μg/mouse) emulsified in complete Freund's adjuvant. Mice were injected intravenously with the liposomal suspension (241 μl) at day 1 of arthritis induction (around day 21 after single immunization with collagen type II). Day one was defined as the day where the inflammation was obvious (clinical score after R. O. Williams of at least 2).

Mice were sacrificed ten hours after the injection of the liposomal suspension. Organs and paws were removed and immediately frozen in liquid nitrogen. The biodistribution of the Cy5.5 labelled CD40 antisense encapsulated in the liposomes was assessed by NIR-Imaging and compared with tissue samples of untreated mice. Specific enrichment was found for inflamed paws in mice with active disease. More specifically, accumulation of the amphoteric liposomes coincides with the highly active sites of the disease on individual paws or even toes or fingers (see FIG. 7).

Example 9 Preparation of CD40-ODN-Containing Liposomes with the Advanced Loading Procedure

Liposomes were produced by injecting 10 Vol-% of an ethanolic lipid solution (a mixture of 15 mol. % POPC, 45 mol. % DOPE, 20 mol. % MoChol and 20 mol. % CHEMS) into 10 mM NaAc 50 mM NaCl pH 4.5 containing 60 μg/ml of a 18 bp antisense against CD40.

The resulting lipid concentration was 2 mM. The pH of this solution was immediately shifted with 1/10 volume 1M Hepes pH 8. To concentrate the diluted liposomes the suspensions were sedimented for 2 h and 5 min at 65,000 rpm at 20° C. in a T865 rotor (Sorvall Ultra Pro 80). Afterwards the formulation was sterile filtered through 0.45 μm.

TABLE 9 example for Smarticles formulation which encapsulate CD40 ODN Lipid Mol. % size Polydisp. Index POPC/DOPE/MoChol/CHEMS 15:45:20:20 178.5 0.317

The amount of encapsulated ODN was measured by checking the optical density (OD) by 260 nm. The following amount of ODN was encapsulated in the Smarticles formulation.

TABLE 10 encapsulated amount of ODN in the Smarticles formulation μg Encapsu- ODN/μmol lation Lipid Mol. % lipid efficacy POPC/DOPE/MoChol/CHEMS 15:45:20:20 8.87 29.58%

Example 10 Therapeutic Efficacy in Arthritis

DBA/1 mice were immunized by subcutaneous injections of type II collagen (200 μg/mouse) emulsified in complete Freund's adjuvant. Treatment with Smarticles or controls was initiated at day 1 of arthritis induction (around day 21 after single immunization with collagen type II) and repeated at day 3 and 5. Day one was defined as the day where the inflammation was obvious (clinical score after R. O. Williams of at least 2).

For the treatment studies the liposomal CD40-ODN was injected intravenously into the tail vein of rats with established inflammation. Each dosage contains 4 mg CD40-ODN per kg bodyweight (encapsulated CD40-ODN).

During the experiment the swelling of paws were observed and the clinical arthritis score were determined.

As evidenced by FIGS. 8 and 9, there was a significant reduction of the swelling of the paws after a treatment with CD40-ODN encapsulated in the amphoteric liposomes. Also the clinical score was significant reduced after treatment with CD40-ODN encapsulated in such liposomes.

Example 11 Materials

This example provides non-limiting examples of CD40 nucleotide sequences that may be targeted by oligonucleotides that modulate the expression of CD40 and that are suitable for use in the compositions in accordance with the present invention.

Human CD40 mRNA (GenBank accession no. X60592)

Human CD40 mRNA sequence for targeting in accordance with the present invention is presented in SEQ ID NO: 1. Related sequence information is found in published patent application number US 2004/0186071 (i.e., SEQ ID NO: 85) to Bennett, et al. and in U.S. Pat. No. 6,197,584 (i.e., SEQ ID NO: 85) to Bennett, et al. and in Pluvinet, et al., Blood, 2004, 104(12), 3642-3646, the contents of which are incorporated by reference herein.

(SEQ ID NO: 1): 1 gcctcgctcg ggcgcccagt ggtcctgccg cctggtctca cctcgccatg gttcgtctgc 61 ctctgcagtg cgtcctctgg ggctgcttgc tgaccgctgt ccatccagaa ccacccactg 121 catgcagaga aaaacagtac ctaataaaca gtcagtgctg ttctttgtgc cagccaggac 181 agaaactggt gagtgactgc acagagttca ctgaaacgga atgccttcct tgcggtgaaa 241 gcgaattcct agacacctgg aacagagaga cacactgcca ccagcacaaa tactgcgacc 301 ccaacctagg gcttcgggtc cagcagaagg gcacctcaga aacagacacc atctgcacct 361 gtgaagaagg ctggcactgt acgagtgagg cctgtgagag ctgtgtcctg caccgctcat 421 gctcgcccgg ctttggggtc aagcagattg ctacaggggt ttctgatacc atctgcgagc 481 cctgcccagt cggcttcttc tccaatgtgt catctgcttt cgaaaaatgt cacccttgga 541 caagctgtga gaccaaagac ctggttgtgc aacaggcagg cacaaacaag actgatgttg 601 tctgtggtcc ccaggatcgg ctgagagccc tggtggtgat ccccatcatc ttcgggatcc 661 tgtttgccat cctcttggtg ctggtcttta tcaaaaaggt ggccaagaag ccaaccaata 721 aggcccccca ccccaagcag gaaccccagg agatcaattt tcccgacgat cttcctggct 781 ccaacactgc tgctccagtg caggagactt tacatggatg ccaaccggtc acccaggagg 841 atggcaaaga gagtcgcatc tcagtgcagg agagacagtg aggctgcacc cacccaggag 901 tgtggccacg tgggcaaaca ggcagttggc cagagagcct ggtgctgctg ctgcaggggt 961 gcaggcagaa gcggggagct atgcccagtc agtgccagcc cctc

Mus Musculus CD40 mRNA

Murine CD40 mRNA sequence for targeting in accordance with the present invention is presented in SEQ ID NO: 2. Related sequence information is found in published patent application number US 2004/0186071 (i.e. SEQ ID NO: 132) to Bennett, et al., the contents of which are incorporated by reference herein.

(SEQ ID NO: 2): gcctcctggc ccttcagctg tggtctttcc cgttttctga ctttgcggtg acactgggga 60 cttccttaga cctctctgga gacgctttcg gttctgcaga gattcccagg ggtattgtgg 120 gtggggtggg gtaacaatag tgtccctgtg gcgctcccag tccctatagt aatccttcac 180 cectctgcta tcttgcaatc aggagagtcc ttagccctgc tataggtggc ttttgaggtc 240 ctggatgcga ggagggggac tggggggtgg gtcgggtaat gtaagaaaag ggctcctttt 300 gggaccctgg ctcctccagc caccttggtg cccatccctt aaactcttgg ggacaatcag 360 actcctggga aggtcctggg gaaatccctg ctcagtgact agccataggc ccaccgcgat 420 tggtgcccga agaccccgcc ctcttcctgg gcgggactcc tagcagggac tttggagtga 480 cttgtggctt cagcaggagc cctgtgattt ggctcttctg atctcgccct gcgatggtgt 540 ctttgcctcg gctgtgcgcg ctatggggct gcttgttgac agcggtgagt ggcttgtgtt 600 ctaacctcca agggagttag ggcttagaga gtgagagatg gaaagaggaa agaggagaca 660 agactttgga gatgagagat cttcctactg gaagcggcgg ttagtaggat gggcaagatc 720 tctcgcgtct tgacacacac acacacacac acaaatgagg tgggctgctc ctctttcctt 780 ccagaaggtc ggggttctgt tccacgaagc ccacagggaa ccttagggag ggcattcctc 840 cacagcggtg cctggacagc tttgtctgac ccaagccttg ctccggagct gactgcagag 900 actggaaagg gttagcagac aggaagcctg gctggggg 938

Rat CD40 mRNA (GenBank Accession No. AF 241231)

Rat CD40 mRNA sequence for targeting in accordance with the present invention is presented in SEQ ID NO: 3. (See, Gao, Ph.D. thesis, Goettingen 2003).

(SEQ ID NO: 3): 1 tgggacccct gtgatctggc tgctctgatc tcgctctgca atgctgcctt tgcctcagct 61 gtgcgcgctc tggggctgct tgttgacagc ggtccatcta ggacagtgtg ttacgtgcag 121 tgacaaacag tacctccaag gtggcgagtg ctgcgatttg tgccagccgg gaaaccgact 181 agttagccac tgcacagctc ttgagaagac ccaatgccaa ccgtgcgact caggcgaatt 241 ctcagctcac tggaacaggg agatccgctg ccaccagcac cgacactgcg aactcaatca 301 agggcttcag gttaagaagg agggcaccgc ggtntcagac actgtttgta cctgcaagga 361 agggcagcac tgcgccagca aggagtgcga gacgtgcgct cagcacaggc cctgtggccc 421 tggctttgga gtcgtgcaga tggccactga gactactgat accgtctgcc aaccctgccc 481 ggtcggattc ttctccaatg ggtcatcact ttttgaaaag tgtcatccat ggacaagctg 541 tgaagat

Porcine CD40 cDNA

Porcine CD40 cDNA sequence for targeting in accordance with the present invention is presented in SEQ ID NO: 4. (FIG. 10). Related sequence information is found in Rushworth, et al., Transplantation, 2002, 73(4), 635-642, the contents of which are incorporated by reference herein.

In addition, the following provide non-limiting examples of anti-CD40 oligonucleotides, e.g., antisense CD40 nucleic acid sequences, that are suitable for use in the present invention:

Oligonucleotides Against Human CD40

Examples of human antisense CD40 oligonucleotides are presented below. Further sequence information is found in published patent application number US 2004/0186071 and U.S. Pat. No. 6,197,584 to Bennett, et al., the contents of which are provided by reference herein. The SEQ ID NOS. referred to by Bennett, et al. are provided to the right.

SEQ ID NO: 5 ccaggcggca ggaccact Seq ID No: 1 of Bennett et al.   SEQ ID NO: 6 gaccaggcgg caggacca Seq ID No.: 2 of Bennett et al. SEQ ID NO: 7 aggtgagacc aggcggca Seq ID No: 3 of Bennett et al. SEQ ID NO: 8 gcagaggcag acgaacca Seq ID No: 5 of Bennett et al. SEQ ID NO: 9 gcaagcagcc ccagagga Seq ID No: 6 of Bennett et al. SEQ ID NO: 10 ggtcagcaag cagcccca Seq ID No.: 7 of Bennett et al. SEQ ID NO: 11 gacagcggtc agcaagca Seq ID No: 8 of Bennett et al. SEQ ID NO: 12 gatggacagc ggtcagca Seq ID No: 9 of Bennett et al. SEQ ID NO: 13 tctggatgga cagcggtc Seq ID No: 10 of Bennett et al. SEQ ID NO: 14 ggtggttctg gatggaca Seq ID No: 11 of Bennett et al. SEQ ID NO: 15 gtgggtggtt ctggatgg Seq ID No: 12 of Bennett et al. SEQ ID NO: 16 gcagtgggtg gttctgga Seq ID No: 13 of Bennett et al. SEQ ID NO: 17 ctggcacaaa gaacagca Seq ID No: 15 of Bennett et al. SEQ ID NO: 18 gtgcagtcac tcaccagt Seq ID No: 20 of Bennett et al. SEQ ID NO: 19 attccgtttc agtgaact Seq ID No: 23 of Bennett et al. SEQ ID NO: 20 ttcaccgcaa ggaaggca Seq ID No: 25 of Bennett et al. SEQ ID NO: 21 ctctgttcca ggtgtcta Seq ID No: 26 of Bennett et al. SEQ ID NO: 22 ctggtggcag tgtgtctc Seq ID No: 27 of Bennett et al. SEQ ID NO: 23 ggtgcccttc tgctggac Seq ID No: 31 of Bennett et al. SEQ ID NO: 24 ctgaggtgcc cttctgct Seq ID No: 32 of Bennett et al. SEQ ID NO: 25 gtgtctgttt ctgaggtg Seq ID No: 33 of Bennett et al. SEQ ID NO: 26 acaggtgcag atggtgtc Seq ID No: 35 of Bennett et al. SEQ ID NO: 27 gtgccagcct tcttcaca Seq ID No: 37 of Bennett et al. SEQ ID NO: 28 tgcaggacac agctctca Seq ID No: 40 of Bennett et al. SEQ ID NO: 29 gagcggtgca ggacacag Seq ID No: 41 of Bennett et al. SEQ ID NO: 30 aatctgcttg accccaaa Seq ID No: 43 of Bennett et al. SEQ ID NO: 31 gctcgcagat ggtatcag Seq ID No: 46 of Bennett et al. SEQ ID NO: 32 gcagggctcg cagatggt Seq ID No: 47 of Bennett et al. SEQ ID NO: 33 gactgggcag ggctcgca Seq ID No: 49 of Bennett et al. SEQ ID NO: 34 gcagatgaca cattggag Seq ID No: 52 of Bennett et al. SEQ ID NO: 35 tcgaaagcag atgacaca Seq ID No: 53 of Bennett et al. SEQ ID NO: 36 gtccaagggt gacatttt Seq ID No: 54 of Bennett et al. SEQ ID NO: 37 caggtctttg gtctcaca Seq ID No: 57 of Bennett et al. SEQ ID NO: 38 ctgttgcaca accaggtc Seq ID No: 58 of Bennett et al. SEQ ID NO: 39 gtttgtgcct gcctgttg Seq ID No: 59 of Bennett et al. SEQ ID NO: 40 gtcttgtttg tgcctgcc Seq ID No: 60 of Bennett et al. SEQ ID NO: 41 caccaccagg gctctcag Seq ID No: 64 of Bennett et al. SEQ ID NO: 42 gggatcacca ccagggct Seq ID No: 65 of Bennett et al. SEQ ID NO: 43 gtcgggaaaa ttgatctc Seq ID No: 71 of Bennett et al. SEQ ID NO: 44 ggagccagga agatcgtc Seq ID No: 73 of Bennett et al. SEQ ID NO: 45 tggagccagg aagatcgt Seq ID No: 74 of Bennett et al. SEQ ID NO: 46 tggcatccat gtaaagtc Seq ID No: 77 of Bennett et al. SEQ ID NO: 47 ggtgcagcct cactgtct Seq ID No: 81 of Bennett et al. SEQ ID NO: 48 aactgcctgt ttgcccac Seq ID No: 82 of Bennett et al.

The following siRNA sequences are suitable for use in the present invention. (See, e.g., Pluvinet, et al., Blood, 2004, 104(12), 3642-3646), the contents of which are incorporated by reference herein.

(SEQ ID NO: 49): 5_-GCGAAUUCCUAGACACCUGUU-3_ (siRNA-2 of Pluvinet 3_-UUCGCUUAAGGAUCUGUGGAC-5_ et al.) (SEQ ID NO: 50): 5_-CUGGUGAGUGACUGCACAGUU-3_ (siRNA-6 of Pluvinet 3_-UUGACCACUCACUGACGUGUC-5_ et al.) (SEQ ID NO: 51): 5_-UACUGCGACCCCAACCUAGUU-3_ (siRNA-8 of Pluvinet 3_-UUAUGACGCUGGGGUUGGAUC-5_ et al.)

All siRNA contain a 2 nucleotide overhang at 3′ends.

Oligonucleotides Against Murine CD40

Examples of murine antisense CD40 oligonucleotides are presented below. Further sequence information is found in published patent application number US 2004/0186071 to Bennett, et al., the contents of which are hereby incorporated by reference herein. The SEQ ID NOS. referred to by Bennett, et al. are provided to the right.

Murine

SEQ ID NO: 52 agacaccatc gcag Seq. ID No. 116 of Bennett et al. SEQ ID NO: 53 gcgagatcag aagag Seq. ID No. 117 of Bennett et al. SEQ ID NO: 54 cgctgtcaac aagca Seq. ID No. 118 of Bennett et al. SEQ ID NO: 55 ctgccctaga tggac Seq. ID No. 119 of Bennett et al. SEQ ID NO: 56 ctggctggca caaat Seq. ID No. 120 of Bennett et al. SEQ ID NO: 57 cttgtccagg gataa Seq. ID No. 123 of Bennett et al. SEQ ID NO: 58 cacagatgac attag Seq. ID No. 124 of Bennett et al. SEQ ID NO: 59 tgatatagag aaaca Seq. ID No. 125 of Bennett et al. SEQ ID NO: 60 ctcattatcc tttgg Seq. ID No. 127 of Bennett et al. SEQ ID NO: 61 ggttcagacc agg Seq. ID No. 128 of Bennett et al. SEQ ID NO: 62 tttatttagc cagta Seq. ID No. 130 of Bennett et al. SEQ ID NO: 63 agccccacgc actgg Seq. ID No. 131 of Bennett et al. SEQ ID NO: 64 tctcactcct atcccagt Seq. ID No. 134 of Bennett et al. SEQ ID NO: 65 attagtctga ctcgt Seq. ID No. 138 of Bennett et al. SEQ ID NO: 66 acattagtct gactc Seq. ID No. 139 of Bennett et al. SEQ ID NO: 67 cagatgacat tagtc Seq. ID No. 142 of Bennett et al. SEQ ID NO: 68 ctggactcac cacag Seq. ID No. 143 of Bennett et al. SEQ ID NO: 69 ggactcacca cagat Seq. ID No. 144 of Bennett et al. SEQ ID NO: 70 actcaccaca gatga Seq. ID No. 145 of Bennett et al. SEQ ID NO: 71 tcaccacaga tgaca Seq. ID No. 146 of Bennett et al. SEQ ID NO: 72 accacagatg acatt Seq. ID No. 147 of Bennett et al. SEQ ID NO: 73 agatgacatt ag Seq. ID No. 153 of Bennett et al. SEQ ID NO: 74 cagatgacat tag Seq. ID No. 154 of Bennett et al. SEQ ID NO: 75 acagatgaca ttag Seq. ID No. 155 of Bennett et al. SEQ ID NO: 76 ccacagatga cattag Seq. ID No. 156 of Bennett et al. SEQ ID NO: 77 accacagatg acattag  Seq. ID No. 157 of Bennett et al. SEQ ID NO: 78 caccacagat gacattag Seq. ID No. 158 of Bennett et al. SEQ ID NO: 79 tcaccacaga tgacattag Seq. ID No. 159 of Bennett et al. SEQ ID NO: 80 ctcaccacag atgacattag Seq. ID No. 160 of Bennett et al.

Oligonucleotides Against Rat CD40

Examples of rat antisense CD40 oligonucleotides are presented below. (See, Gao, Ph.D. thesis, 2003, University of Gottingen, Germany).

SEQ ID NO: 81 accgctgtc aacaagcagc (rAS2 of Gao) SEQ ID NO: 82 tcctagatggaccgctgt(rAS3 of Gao) SEQ ID NO: 83 taacacactgtcctag(rAS4 of Gao)

Oligonucleotides Against Porcine CD40

Examples of porcine antisense CD40 oligonucleotides are presented below. See, Rushworth, et al., Transplantation, 2002, 73(4), 635-642, the contents of which are incorporated by reference herein.

SEQ ID NO: 84 gctgatgacagtgtttct Aso3 of Rushworth et al.) SEQ ID NO: 85 gcctcactctcgctcctg (Aso8 of Rushworth et al.) SEQ ID NO: 86 ggactgtatctggactgc (Aso9 of Rushworth et al.) SEQ ID NO: 87 gtggacagtcatgtatat (Aso10 of Rushworth et al.)

The present invention therefore provides formulations of amphoteric liposomes that exhibit improved stability upon contact with mammalian serum, releasing less or no encapsulated drugs. Such liposomal formulations may be useful in the delivery of drugs after a systemic administration into the blood stream. The invention especially suits the delivery of oligonucleotides, a new class of drugs that is currently under development, and DNA plasmids, without being limited to such uses. The majority of such compounds have an intracellular site of action. Carrier systems are used to overcome the poor uptake of such substances and are sometimes an indispensable prerequisite.

Other embodiments and uses of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. All patents, patent applications, and other references noted herein for whatever reason are specifically incorporated by reference. The specification and examples should be considered exemplary only with the true scope and spirit of the invention indicated by the following claims. 

1. A mixture of lipids capable of encapsulating an active agent to form a liposome, said mixture comprising phosphatidylcholine and phosphatidylethanolamine in a ratio of phosphatidylethanolamine to phosphatidylcholine in the range of about 0.5 to about
 8. 2-55. (canceled) 